Members are encouraged to pay for training sessions per term to keep the administrative burden of collecting cash to a minium but some members cannot attend training sessions regularly, so choose to pay per session generally, which is OK.
If you want to come along and try a training session, you can pay per session (£3.50) to begin with, to see how you get on.
Note that the actual costs per term will vary according to how long the term is. This page of the website may become out of date so please just use the costs here as a guide.